激光诱导击穿光谱（LIBS）技术作为一项新兴的水下原位探测技术，备受海洋探测技术领域的关注。将这项技术推向实用化的关键之一是改善LIBS的远程探测能力，因此需要采用超击穿阈值的高能量探测激光。为观察超击穿阈值情况下的等离子体辐射和动态击穿特性，采用图像与光谱相结合的方法，以KCl溶液为样品进行了系列实验研究。通过对1～20mJ不同能量激发下的等离子体图像分析，获得了不同激发条件下总辐射的轴向跨度和最亮点位置信息。随激光脉冲能量增大，等离子体长度增加，从1mJ时的0.49mm增加到20mJ时的1.83mm，同时辐射最亮点位置向激光入射方向移动了0.79mm。结合光谱探测分析，得出等离子体特征辐射的轴向空间分布也对激光能量有明显的依赖性。虽然不同能量下谱线强度呈相似的轴向空间分布，但钾原子辐射最强处的位置和相应强度均随能量变化，在5mJ激发下获得最佳辐射强度。实验结果表明，为满足远程LIBS应用需求，提高激光能量时应考虑其对原子辐射的影响。还对不同能量下的谱线的半高宽和信背比进行了观测分析。%Laser‐induced breakdown spectroscopy (LIBS) ,as a promising in‐situ underwater detection technology ,has received extensive attention in the field of ocean exploration .Improving the remote sensing ability of LIBS is crucial in bringing this tech‐nology into practical applications ,hence higher laser energies ,i .e .over threshold ,are required .To characterize the plasma in‐duced with super threshold energies and have a better understanding of resulted moving breakdown process ,some extensive in‐vestigations into KCl water solution have been carried out with spectra‐image jointed analysis .The spatial span and the brightest spot position of plasma radiation ,with different laser energies from 1 to 20 mJ ,were determined from the recorded plasma ima‐ges .It was found that the plasma stretched from 0.49 to1.83 mm ,as the laser pulse energy increased from 1 to 20 mJ ,with a center position shift of 0.79 mm towards the incident laser beam .The obvious power dependence has also been observed from the obtained spatial resolved atomic spectra .Although the axial distributions at different energies were similar ,both the position and the intensity of potassium atomic emission maximum varied .The optimal laser energy was determined to be 5 mJ with the emis‐sion intensity maximum higher than that at any other investigated energies .The obtained results suggested that the power de‐pendence of atomic emission should be taken into account on increasing laser energy to meet the needs of stand‐off LIBS applica‐tions .The FWHM and signal to background ratio of K Ⅰ 769.90 nm under different laser energies have also been investigated .
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